In case of hydraulic delivery, with the pipe-chamber feeders used for increasing the pressure of the slurry, two or more chambers of similar size and construction are usually operated periodically according to a predetermined rhythm. The operational cycle of one chamber comprises the filling-up of the chamber with low-pressure slurry, then the sluicing to a considerably higher delivery pressure, washing-out of the content of the chamber into delivery duct by means of a high-pressure water jet, and the release of pressure necessary thereafter. The cycle consisting of the above four steps is repeated continuously within one chamber and the time diagram of cycles of the individual chambers is identical. The high-pressure water jet is used as a recycled delivery medium, since the slurry, having a relatively high degree of viscosity, cannot be delivered under high pressure, while water, being used as the recycled delivery medium, can be transported at high pressure.
The basic requirement of the operation of such a known feeder is the continuous flow of the high-pressure slurry in the delivery duct and that the rhythmic operation of the locking mechanisms of the feeder should not cause any appreciable speed or pressure fluctuation. Therefore, in a two-chamber feeder the discharging cycle occupies necessarily one half of the cyclic time. Since the sluicing of pressure occurs in the closed state of the chamber and during this time the chamber cannot be charged, or refilled with fresh slurry, it is obvious that a shorter time is available for charging or refilling of the chamber with slurry, than for discharging it; therefore the filling-up of the two-chamber feeders cannot be continuous.
The detrimental effect of the stagewise filling-up is due to the delivery capacity being reduced, on one hand, and due to the slurry being diluted in the feeder, on the other hand, since in the intervals of the filling-up water is required to be supplied to the delivery duct in order to maintain the flow, a more serious drawback is caused by the intermittent filling up in such cases when the feeder is used as pressure intensifier in a series-connected chain. In this case the low-pressure slurry arrives with a continuous flow; it can be fed, however, only intermittently into the pressure intensifier, and consequently the insertion of a storage tank becomes necessary.
The continuous filling-up is possible with the feeders of conventional construction only when using more than two, or at least three chambers, requiring considerable space and large expenses, due to the chamber lengths being practically several hundred meters.